The optical element mentioned above is, for example, an optical lowpass filter (OLPF) and the like. This optical lowpass filter has a structure disclosed in Patent Document 1. In detail, an optical lowpass filter 110 is structured such that a retardation film 170 that is a type of transmitting optical films is sandwiched by two birefringent plates 150 and 180 that are a type of transmitting optical substrates and made of crystal, as shown in FIG. 11. Members (the birefringent plate 150, an IR-cut glass 160, the retardation film 170, and the birefringent plate 180) constituting the optical lowpass filter 110 are bonded with each other with adhesive layers 190. The optical lowpass filter 110 may have such structure that the IR-cut glass 160 is bonded as a unit. The optical lowpass filter 110 includes a sealant 200 at a peripheral border thereof. The sealant 200 may be formed in a contiguous manner from the end part of the bonding layers 190 or formed so as to cover whole end part of the optical lowpass filter 110.
Optical elements such as the optical lowpass filter 110 are required to have quality reliability in a high-temperature environment test, a low-temperature environment test, a temperature shock test in which a temperature is changed high and low repeatedly, a high-humidity environment test, and the like. Therefore, a pressure sensitive adhesive that is suitable for a temperature shock tends to be employed compared to an adhesive as the bonding layers 190 shown in FIG. 11. In particular, bonding the birefringent plates 150, 180 and the retardation film 170, employs a pressure sensitive adhesive so as to prevent the plates and the film from peeling off from each other due to a difference in their volume contractions caused by a temperature change. The pressure sensitive adhesive has a preferable viscosity function so as to be able to absorb the difference in the volume contractions. The sealant 200 is provided at the end part of the pressure sensitive adhesive or the periphery of the optical element in order to prevent water from permeating.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-309151    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-258165